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Articles by N. Amizuka
Total Records ( 3 ) for N. Amizuka
  S Ubaidus , M Li , S Sultana , P. H. L de Freitas , K Oda , T Maeda , R Takagi and N. Amizuka
 

This study aimed to evaluate whether the immunolocalization of fibroblast growth factor (FGF) 23 and dentin matrix protein 1 (DMP1) is associated with the spatial regularity of the osteocyte lacunar canalicular system(s) (OLCS). Femora of 12-weeks-old male ICR mice were fixed with 4% paraformaldehyde, decalcified with a 10% EDTA solution and then embedded in paraffin. We have devised a triple staining procedure that combines silver impregnation, alkaline phosphatase (ALPase) immunohistochemistry and tartrate-resistant acid phosphatase (TRAPase) enzyme histochemistry on a single paraffin section. This procedure permitted the visualization of ALPase-positive plump osteoblasts and several TRAPase-positive osteoclasts on those bone matrices featuring irregularly arranged OLCS, and of ALPase-positive bone lining cells on the bone matrix displaying the well-arranged OLCS. As observations proceeded from the metaphysis toward the diaphysis, the endosteal cortical bone displayed narrower bands of calcein labeling, accompanied by increased regularity of the OLCS. This implies that the speed of bone deposition during bone remodeling would affect the regularity of the OLCS. While DMP1 was evenly localized in all regions of the cortical bones, FGF23 was more abundantly localized in osteocytes of cortical bones with regularly arranged OLCS. In cortical bones, the endosteal area featuring regular OLCS exhibited more intense FGF23 immunoreaction when compared to the periosteal region, which tended to display irregular OLCS. In summary, FGF23 appears to be synthesized principally by osteocytes in the regularly distributed OLCS that have been established after bone remodeling.

  M Li , Y Seki , P. H. L Freitas , M Nagata , T Kojima , S Sultana , S Ubaidus , T Maeda , J Shimomura , J. E Henderson , M Tamura , K Oda , Z Liu , Y Guo , R Suzuki , T Yamamoto , R Takagi and N. Amizuka
 

The signaling axis comprising the parathyroid hormone (PTH)-related peptide (PTHrP), the PTH/PTHrP receptor and the fibroblast growth factor receptor 3 (FGFR3) plays a central role in chondrocyte proliferation. The Indian hedgehog (IHH) gene is normally expressed in early hypertrophic chondrocytes, and its negative feedback loop was shown to regulate PTH/PTHrP receptor signaling. In this study, we examined the regulation of PTH/PTHrP receptor gene expression in a FGFR3-transfected chondrocytic cell line, CFK2. Expression of IHH could not be verified on these cells, with consequent absence of hypertrophic differentiation. Also, expression of the PTH/PTHrP receptor (75% reduction of total mRNA) and the PTHrP (50% reduction) genes was reduced in CFK2 cells transfected with FGFR3 cDNA. Interestingly, we verified significant reduction in cell growth and increased apoptosis in the transfected cells. STAT1 was detected in the nuclei of the CFK2 cells transfected with FGFR3 cDNA, indicating predominance of the JAK/STAT signaling pathway. The reduction in PTH/PTHrP receptor gene in CFK2 cells overexpressing FGFR3 was partially blocked by treatment with an inhibitor of JAK3 (WHI-P131), but not with an inhibitor of MAPK (SB203580) or JAK2 (AG490). Altogether, these findings suggest that FGFR3 down-regulates PTH/PTHrP receptor gene expression via the JAK/STAT signaling in chondrocytic cells.

  K Narimatsu , M Li , P. H. L de Freitas , S Sultana , S Ubaidus , T Kojima , L Zhucheng , G Ying , R Suzuki , T Yamamoto , K Oda and N. Amizuka
 

Preosteoblasts are currently defined as the precursors of mature osteoblasts. These cells are morphologically diverse and may represent a continuum during osteoblast differentiation. We have attempted to categorize the different preosteoblastic phenotypes in vivo by examining bone cells expressing the runt-related transcription factor 2, alkaline phosphatase and BrdU incorporation – histological traits of a preosteoblast – under transmission electron microscopy (TEM). TEM observations demonstrated, at least, in part two preosteoblastic subtypes: (i) a cell rich in cisterns of rough endoplasmic reticulum (rER) with vesicles and vacuoles and (ii) a subtype featuring extended cytoplasmic processes that connect with distant cells, with a small amount of scattered cisterns of rER and with many vesicles and vacuoles. ER-rich cells, whose cellular machinery is similar to that of an osteoblast, were often seen adjacent to mature osteoblasts, and therefore, may be ready for terminal differentiation. In contrast, ER-poor and vesicle-rich cells extended their cytoplasmic processes to mature osteoblasts and, frequently, to bone-resorbing osteoclasts. The abundant vesicles and vacuoles identified in this cell type indicate that this cell is involved in vesicular transport rather than matrix synthesis activity. In summary, our study verified the morphological diversity and the ultrastructural properties of osteoblastic cells in vivo.

 
 
 
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